Telephone system



Junef24, 1941;

r H. DRI-:YER

TELEPHONE SYSTEM Fild .1u-1y 22, 1937 Fila. 1

4 Sheets-Sheet 1 INVENTOR. HANS DREYER ATTORNEY. l

June 24, 1.941.

H. DREYER TELEPHONE SYSTEM Filed July 22. 1937 4 Sheets-Sheet 2 FIG., 1A

HANS DREY'ER ATTORNEY.

June 24, 1941.

l-yl. DREYER TELEPHONE SYSTEM Filed July 22, 1937 4 Sheets-Sheet 3 -HANS DREYER Patented June 24, 1941 es orties vHansi liheyezs Berlin-Charlottenburg, Germany, l assigner .to Siemens & Halske Aktiengesell- 1 schaft of Wernerwerk, Siemensstadt, near Berlin, Germany Appli-mien July 22, 1937, serial No. 154,981

" in Germany `luly 3i), 1936 13 Claims.

The present invention relates to a circuit` arrangement for control switches in telephone systems. It aims at a better utilization ofthe contacts of the control switch thereby realizing an increase in eliciency in control switch workingl .r'

The-calls initiated over control switches" are so lar as is possible to result in the-establishment oi a call even during peak periods in the traic. ln addition a signal is to be sent to the calling station in the event of the group of lines in the Vdesired traffic direction being engaged without it being necessary to use more 4contacts inthe vcontrol switches y In the known arrangements overflow Vrepeaters were arranged at auxiliary contacts `o i the con-` trol switch which, in the event of 'all the'lines of the group from which if another traii'ic direction had been dialledthe control switch would khave been controlled, being busy, were seized by the control switch. `These, overflow repeaters then '11 transmitted a switching-over signal for controlling the control switch when the digits', characterizing particular traffic directionsv were dialleol.

In the event of a group of linesfcontrolled by an overflow repeater after the `switching over?l operation, being busy, itis necessary to transmit a busy signal to thecalling station.` For this signalling operation the arrangement according to the invention 'uses the same contact set of the i control switch as that rto which the dummy re-L heater is connected. J l p Moreover, the devices which may bereached 'over the overflow positions'of the controlswitch are arranged to receive the characteristic number'` of the desired traiiic direction in such a manner 1 that these devices are associated in common with a plurality of groups of control switches..

.Another advantageous feature of the invention consists in the provision of a Vplurality of groups overow positions, these auxiliary paths containing switching devices (connecting switches) which may be reached directly from the control switches of other groups of lines.

In Figs. l, 1A, 2, and 2A embodiments of the invention are shown, the latter not being limited to these embodiments. Only the details necessary for understanding the invention are shown. Figs. l and 1A, when placed side by side, show two control switches D and DI having access in common to a repeater UGW for outgoing calls, to a selector switch JGW for local calls and to an overflow device BL.

Figs. 2 and 2A, when placed side by side, show a control switch EDI normally having access only vto certain switching selectors, such as UGWII and to certain local selectors, such as JGWIGI; a similar control switch IDII is shown normally having access only to different switching selec- I tors, 'such as UGWSII and to different local selectors, as J GW l G11. Also shown are two changeover circuits WeI and WcII by means of which either control switch may gain accessto a switching` selector or a local selector normally accessible only to the other control switch.

Referring now particularly to Figs. 1 and 1A, when a calling station initiates a call the switch D after having been seized over selecting devices whichare 'not shown sets itself on a freev device lUGrW-by a free stepping operation. During this setting the switch D is controlled over wiper cd. After the repeater UGW` has been connected up thesubscriber receives dial tone in the known The subsequent dialling determines whether the call is to proceed over the repeater UGW or whether the switch D must bring about the switching `operations in orderto connect up a'free device JGW. If the calling station dials the number of an exchange which is reached over the line La? and Lb'i the call is set up in known way over this line. If, however, the subscriber dials `a digit characterising internal calls a control impulse is transmitted over the line Ld2 by devices in the control repeater UGW, whereupon the switch D searches for a free group selector of control switches such that ,control repeaters w JGW linde? the control of wiper dd.

are reached over the (Werf-10W ,positions 0f the If WhEIl a @all S initiated 2.11 the Outgoing l'leS control switches of one groupof lines which can which lealuto the control repeater UGW are er1- be reached directly from another group or conj eased the Wipers 0f the SWtCh D DaSS t0 pOS'GOn trol switches and have access to ,succeeding de-A s'5- ln this DOSOH ,a deVCe DTOVded With a Viceg t numerical impulse receiver is seized over wiper ln place of busy repeating devices, in the event "yhs deVCe being S0 CODSIUC'GBdha the Calloi all the lines of a group which are reached Aafter ing Stan receives the bllSYSgnJ if an external o, switching over operation being `lousyy auxiliary 'traffic directionhas been dialledto indicate that paths can conveniently be connected up at the 0 9.11 the lines in this direction are engaged- If,

however, the calling stationV dials `an internal number the device seized over cd in position Il up in order `to connect up a free connecting path in the desired direction under the control of wiper dd. If a free path in this direction is not .found the switch can again pass to position I'I from which it has already been advanced. In this position the calling station now receives a busy signal. On the call being abandoned the switch D is advanced Vfrom position l? to position O. If when'the call is initiated a free control repeater UGW is found by the switch D and this performs its switching-over operation the calling station similarly receives a busy signal when the switch D is set in position Il if the latter has not previously found a free internal group selector.

The device which is reached over position Il can be provided in common for a plurality of switches. Figs. l and 1A show such a device associated with two groups (I and II) of switches, one switch of each group being shown. The switch of the group I has the reference D and the switch of the other group II has the reference DI The switches of the group II are constructed in the same way as the switches of the group I and Hg and earth. In this circuit relay lR energizes and operates contacts lr, 2r, and 3T. The testing wiper cdof the switch D is connected up by contact Ir. The interrupter device U11. is connected to the rotary magnet Dw of the switch over contacts 2r and 4t. The magnet Dw receives impulses from the repeater Un so that the wipers ad, bd, cd, del and ed are advanced step- Wise. Contact 31" prepares for the connection of Winding I of relay U. When the switch D finds a Vfree line yin the group to be tested over wiper cd,

for example the line La2-Ld2, the following testing circuit is established: earth, battery (not v shown), lead Lc, windings I and II of relay T,

Acontact 9u, winding II of relay R, contact Ir, wiper ed, lead Lc2, common switching means in the `control repeater UGW, which are not shown and earth. In this circuit relay T and other switching means in the lead L02, which are not shown. energize.

The switch D is brought to rest by the opening of contact 4t. Contact 5t shortcircuits winding I of relay T. Cont-acts Gt and It switch through the leads La and LbI (the speaking leads). The circuit for winding I of relay R is broken at contact 5t, but the relay does Anot Vrelease since its winding II holds up in series with winding II of relay T.A The calling subscriber now receives dial tone in the known manner whereupon he transmits the impulse train or trainsv forming the call number. The impulses produced at the calling station are `taken up by relay A and are transmitted to succeeding de- .vices in the known way. Relay B remains up Vduring theimpulse transmission over the leads La-LaZ and Lb-Lb2. When the impulses are received by relay A a switching device for example .a discriminator switch (not shown) in the control repeater UGW is operated and effects certain switching operations if particular numbers .are dialled. If the calling station dials digits characterizing a call passing over the line La2, Lb2 (external) the special switching device in CJI the repeater UGW does not effect any switching operation. After dialling numbers which characterize an internal call, however, the contact st is temporarily closed by the switching device arranged in the control repeater UGW. This applies earth to lead LdZ whereby relay U in the switch `D is energized yin vthev following circuit: earth, contact st, lead Ld2, wiper dd, windings III and II of relay U. contact 5t, lead Lc, battery (which is not shown) and earth. Relay U oper- -ates yits contacts and at contact 9u breaks the connection between leads Lc and L02. The device UGW'is thereby released. Relay T releases immediately while relay R does not since it is a slow-to-release relay. Relay R establishes a locking circuit over its winding I passing over contact 5t, winding v4I of relay R and the operated contact I'u to resistance Wil and earth. After relay T has released contact t is closed so that the magnet Dw receives impulses from the interrupter Un, .Relay Uis connected to earth over its winding I and contacts 3T and 8u and is thus held energized by the battery applied to lead Lc. When the switch D finds a free line, for example La3-Ld3 in the group tested over the wiper dd, the following testing circuit is established: battery, lead Lc, windings I and II of relay T, contact 9u, winding III of relay U, wiper dd', lead Ld3 and earth. Relay T brings the switch D to rest by opening contact 4t and by closing contacts lit and 'It switches the leads La and Lb through. The switching over of contact 5t guards the line which has been found. Relay R is deenergized, its circuit being broken at contact 5t. Relay U, however, remains energized over wiper dd. The calling station is now in the position to deenergize relay A2 intermittently bytransmitting impulses and to control switches which are not shown, relay B2 remaining operated.

If the call is to be released this can be brought aboutby ydisconnecting the battery connected to lead Lc whereupon relays T and U release. Through the closing of contact 4t the magnet Dw is again connected'to the interrupter Un, whereupon the switch is stepped until wipers ad to ed reach position O. The release can just as well be brought about by breaking the 4lead Ld3 in dependence upon relays A2 and B2.

If the switch D is started up by a call at a moment at which free lines (control repeaters) cannot be reached over wiper fed, the switch D is advanced to position II. In this position the following testing circuitA is s et up: earth, switching means in the repeater device BL, which are not shown, contact I4g/l, relay Xl, lead L04, wiper cd in position H, contact lr, winding II of relay R, contact 9u windings II and I of relay T, lead Lc, battery and earth (not shown) on the lead Lc. In this circuit relays T and Xl energize. Relay T brings the switch D to rest in the manner already described. Relay R holdsup over winding II. Relay XI operates contacts 14ml, |5c| and Il. Contacts Mr! and |5rrl serve to connect the leads Lad and Lb4 to relays A3 and B3. lContact |632! connects lead Ld to contactl 22ug. v

A signal is transmitted to the calling station indicating thatvdialling can commence. Relays B3 and A3 are energized over the loop between leads La and Lb. 'When the dial switch is operated at the calling station relay B3 holds up while relay A3 is impulsively deenergized by the breakages in the loop which occur during impulsing at `the calling station. Through the energizing of. relays A3 and B3 when the calling station is connected to the device BL, contacts |1a3, |8123 and |9133 are operated. Sincecontact |'|a,3 opens before contact Ib closes the rotary magnet CH of the stepping switch disposed in the device BL is not energized. Contact |9123 disconnects the interrupter Un2. When now the calling station operates the impulse sending device, the rotary magnet' CI-Iand the slow relay V are energized by the intermittent closing of contact Het. The rotary magnet CI-I steps lthe wipers 20h and lich. Bela-yV which is a slow-.torelease relay does not release during the stepping of the switch CH. `Consequently contact 2th) remains open during the reception of an impulse train. When the impulsing is over` relay A3 remains energized for a prolonged period. This causes relay V to release. RelayV `closes contact 20o so that earth is 'connected to wiper 20h. According to the 'setting of switch CH either relay BE or relay UG is now energized. If the switch CII has been'set by the digit 2 for example, relay BE energizes on releaseof contact 2do. Relay BE operates contact 2|be so thatthe busy signal `Bes is connected to windingy II of relay A3 over contact Zibe Yand the condenser Ko. This busy signal is transmitted inductively to winding I of relay A3 so thatthe calling station receives the busy signal; `The calling station only receives this busy signal after diallingacall number which characterizes a `trahie direction (external) which was tested (over wiper cd) unsuccessfully when the call .wasginitiated If, however, after the device BL has been connected up the subscriber vdials the digit which characterizes an internal call, wiper Ech of switch CH passes to position.` l In thisposition relay UG is energized after relay V has released'. `Relay UG closes contact 2311.9 thereby `applying earth over contacts 221,50 and irrl', lead-Lad and wiper dd of windings III and II of relay U. Relay U thereupon energizes in themanner alreadyA described. The switch D is started up again and tests for a free internal connecting line `under the control of wiper dd. i.

rI'he setting of the switch CH in therest position takes place on the deenergization of relays A3 and B3 in that thel interruptor UnZ is then connected over the contact'bank'and wiper lich to the magnet CH through the "closing of contact N193. In this circuit relay V isV energized again so that the earth connected to wiper; 20h/s disconnected at contact 2do. 'Ihe switch'then proceeds to position O, withoutinfluencing any switching means during its stepping. In position O the circuit for the magnet CH and r'elay V is broken at lich. @n vthe further stepping of the switch D relay Xi is' also deenergized if this is to be switchedover onto local lines so that'the busy signal repeater Uei may befseized over contact Mimi by the operation ofrelay Y; It is obvious that instead of the switch CH,` which is only diagrammatically represented andl .which selects the traffic direction by means of an impulsev train, a switch may be provided which differentiates between the traffic directions aftera'plurality of digits have been dialied. 1

If after the transfer operations justdes'cribed the switch D does not und a free line among the internal lines, it is brought to rest in position Il in which relay Yi is energized.4 Itelay YIth'en operates its contacts and connects the transformer Tri to leads Lad and L54 over contacts |231! and i-Eiyi.A The calling 'subscriberreceives 'the busy signal from the transformerover `leads La and Lb. When the connection is released by the disconnection of battery from lead Le after the busy signal has been transmitted, relays T and U in the switch D release. In the repeater Uel relay YI releases. rIhe switch D passes to position O in the manner already described. While the repeater device Uel is transmitting the busysignal contact |lly| is open so that relay XI cannot energize and thus the transmission of the busy signal cannot be interfered with.

If the busy signal repeater Uel is seized by a switch of the group I the repeater BL can be connected up over a switch of group II and can bring about the switching over operations and the transmission of the busy signal. Also the busy signal repeater U62 can transmit a busy signal during the time that the busy signal re.- peater Uel is in operation. l f

If a switch of the group II, for example switch Di, is operated after a control repeater UGW has been reached over this switch and if it does not find a free internal line after the wiper dd has been connected up relay Y2 is energized over contact 281:2 when the switch is brought to rest in position l?. Switch DI is brought to rest in the same way as described in connection with the switch D cigroup I. Relay Y? on energizing, operates contacts 23112, @M2 and 321/2. The calling station receives the busy signal over contacts 2y2 and Sr/2, while by the opening of contact 3|y2, relay X2 is prevented from energizing and this prevents the transmission of busy tone being interfered with by the repeater U62. Ii a switch in group II does not find a free control repeater UGW when a call is initiated, relay X2 is `energized when the switch (for example switch Dl is set in position il, over wiper cd2. Relay X2 then switches through the leads associated with wipers cd2 and b'dZ over contacts 23:62 and Z'lsc, whereupon the overflow repeater BL causes a busy signal to be transmitted after the characterizing impulse train has been received if an external call is characterized, or produces a control signal if an internal call is characterized. The switching operations' which take piace are the same ashave been described in connection with the setting of the switch D of the group I.

In Figs. 2 and 2A another embodiment of the invention is shown. iDI represents a control switch which is equipped similarly to the switch D in Fig. I. This is a switch belonging(` to a gro-up of similar switches referred to by the reference I. In contradistinction to the switch D in Fig. l this switch does not possess a rest position. The special overflow position of this switch is not situated at the end of theI Contact bank but in the middle. This position is indicated by the reference '5. A ten-point switch is shown but the switch can possess either more or fewer contacts. In the left hand bottom corner of the drawings a further switch is shown which is similar in its construction to the switch iDI. This switch has the reference IDII and belongs to a group of switches II. Over the switch IDI and EDII switching group selectors and internal group selectors are reached. On initiating a call the switches IDI or IDII are set on a switching group selector whereupon the transmission of an exchange characterizing digit on the part. of the calling station determines whether tbe call is to proceed over the switching group selector or whether an internal group selector is to be seized by switchingl operations at the switches lDI or iDII. The switching group selectors have the reference UGW and the internal group selectors the reference JGW. The addition of a Roman number indicates over which group of control switches the corresponding group selectors can be reached directly. Over the overow position 6 the control switches have access both to switching group selectors and also to internal group selectors. These switching and internal group selectors reached over the overflow positions of the switches of group I may also be reached over control switches of another group, for example of group II. The connecting of a control switch or an internal group selector over an .overiow position of the control switch is efiected by a change-over circuit indicated by WeI for the group I of control switches and WeII for the group II of control switches.

When the switch IDI is seized by a calling station it is set on a free switching group selector UGWII to UGWEII. The setting of the switch IDI is initiated by the energizing of relay R over winding I. This relay energizes in the following cir-cuit on the connection of battery (not shown) to lead Lc: earth, battery, lead Lc, contact t,

winding I of relay R, contacts Illu and IIg and earth. Relay R energizes and starts up the switch by energizing the rotary magnet IDW over contact 2r. Contact Sr connects winding I of relay U to lead Lc in preparation. Contact Ir prepares for the testing operation by connecting windings I and II of relay T to wiper cd1. When the switch IDI finds a free switching group selector, for example, the switch UGWQI, the following testing circuit is established: battery on lead Lc, windings I and II of relay T, contact 9u, winding II of relay R, Contact Ir, wiper cd1 in position d, seizing means and earth (not shown) in the switching group selector UGWI. i

Relay T energizes and Iby opening contact 4t brings the switch IDI to rest. Contacts Gt and It switch through speaking leads while contact 5t guards the switch which has been found by short-circuiting winding I of relay T. Moreover, contact 5t connects winding I and III of relay U to wiper ddl. When now the calling station operates lthe dial switch a discriminator, known per se, is started up in the switching group selector UGWIlI, the setting of which determines whether the call is to pass over the switching group selector or whether an internalconnecting line is to be connected up by controlling the switch IDI. If in the case of the present call the number characterizing an internal call is dialled earth is temporarily `connected to contact of wiper dcZI, by the discriminator switch in the switching group selector UGWI. Relay U in the switch IDI is consequently energized. Relay U operates contact 8u and thus establishes a lock ing circuit for winding I of relay U Via the lead Lc. Relay T is deenergized because itsV circuit is broken at Contact tu. Relay R which is a slowto-release relay holds up over winding I and the back Contact 5t and contact Illu which has been switched over meanwhile. The rotary magnet IDW is subjected to current over contact lit so that the wipers of the switch IDI are advanced stepwise by the magnet IDW. The switch IDI does not test on contact 6 by way of wiper dcZI during this stepping because the lead LdI is broken at contact I97'nI. The switch passes to position 'I and can search for a free internal group selector belonging to the group I over this position and the following positions 8, 9 and III. If it nds, for example, the internal group selector JGWIIBI to be the iirst free switch relay T energizes in the following circuit: earth (not shown) on lead Ldlil in the group selector JGWIIJI, contact III in the contact bank. as so-v ,ciated with wiper ddI, winding III of relay U, :.contactu, windings II and I of relay T andV battery `on the lead Lc. Relay T energizes and at contact 4t breaks the stepping circuit of the switch IDI and at contacts Bt and It switches through the calling line. The line which has been found is guarded by contact Et; relay R releases. Relay U, however, remains energized.

Other switching `.iperations occur if when a call -is initiated all the outgoing lines in the group rto. be tested are engaged. In this case fthe overflow'position (contact 6) in the switch IDI is used. If, for example, all the switching group selectors of group I of the controlling 'switches are engaged relay EXI is energized over contacts operated when the group selectors are taken into use, for example, over contacts IugwI, etc. Relay EEG has closed contact I8'ex1'. In this case the switch IDI steps until `wiper cd1 finds contact 6. It is immaterial from switch IDI reaches position 6 the following circuit is set up: battery, lead Lc, windings I', I-I of relay T, contact 9u, winding II of relay R, contact Irwipe'r cd1, contact 6, lead Lol, contacts 186ml andl IIy,'relay X, lead L03, switching means connected to lead L05, which are not shown, andearth. I

In thisv circuitrelay T energizes in the switch IDI and brings the switch to rest while switching through the speaking leads. Relay X also energizesand operates contacts |250, I3 and Il'. The switching over of contact lex prevents the internal group selector JGWIGII from being seized over the auxiliary rest position 6 of the switches of group I. Moreover, it causes lead Ld3 'to be connected Ito contact 6 at wiper ddI over which the control impulse is later to be transmitted.' The calling station is now connected to the switching group selector UGWSII which can be reached directly over contact 5 of the control switches of group II: Only one of `these control switches of group II is shown,

'B3 in th switching group selector UGWSII are energized by the loop established by the calling station between leads La and Lb. The relays A3 and B3'operate their contacts. Relay A3 operatin'g slightly before relay B3. Contact ZIlaB opens slightly before contact 22123 closes. Contact 23113 disconnects the interrupter UnZ from the bank of wiper 3s ofthe discriminator switch MS at the switching group selector UGW5II. The group selector UGWSII itself is not shown. It can be a switch of any known construction. Its setting is eiected under the control of relay A3 which also sets the discriminator switch MS.

Relay B3 remains energized during the impulsin'g on the part of the calling station. Relay A3, however, responds to the impulses. Each time the relay A3 releases the stepping magnet S of the discriminator switch MS receives current so -that the discriminator switch takes a step foraimee being received. Ii the subscriber dials an exchange number characterizing an external call, the call passesover the wipers ofthe switching group selectorconnected to leads La and Lb without the dlscriminator switch MS exercising anyswitching function.

On the termination of the characterizing impulse train relay V releases, whereupon `contact 2lb is closed. To the contacts of wiper 2s which are reached if an external traffic direction is dialled no switching means are connected. Obviouslyafter fthe setting of the switching group selectorA which is not shown on a diierent connecting line switching means can become operative to disconnect potential from the stepping magnet S so that subsequent impulse trains which influence relay A3 for the purpose of setting succeeding switches no longer produce a setting of the discriminator switch MS.

If, however, the subscriber dials a digit for setting the discriminator switch which is characteristic of an internal call wiper 2s of the discriminator switch is set on contact 4. When relay V releases at the end of this characterising impulse train relay UG is energized in the following circuit: earth, contact 2Iv, wiper 2s, relay UG, battery and earth. Relay UG energizes and closes contact 2day. Earth is consequently applied to the lead Ld whereupon relay U is energized in the switch IDI. Relay U now influences the switch IDI in the manner already described so that the switch searches for a free outgoing line leading to an internal group selectory over wiper ddI, relay T being deenergized. Through the opening ci the speaking leads at contact Bt and 'it when the switch IDI is advanced from position 5, relays A3 and B3 in the switch group selector UGWEII are deenergized. Hereupon the interrupter UnE is connected to the rotary magnet S and relay V over contacts 23173 and wiper 3s. The rotary magnet S now receives impulses, relays V being energized, until wipers 2s and 3s have reached position O. When wiper 2s leaves position i relay UG deenergizes so that contact 2day is opened. When the switch IDI is advanccd from Contact ti or When contact 9u is switched over relayX is deenergized. Contacts |29: and Ix are consequently opened and contact Illfc closed (normal position). It is clear that when the wipers 2s and 3s are set in the rest position the numerical impulse receiver connected to LaS and Lb is released.

When after the switch IDI has been set on oneof the contacts I to e switching over takes place a free line is sought over contacts I to III of switch IDI, wiper ddll `being connected up. If there are no free lines connected to these contacts the switch IDI tests in position 6. In this position the following circuit is established: battery, lead Lc, windings I and II of relay T, contact Qu, winding III of relay U, wiper ddI, contact I5, lead Ldl, contact Ilix, contact I97`1LI, relay Y, lead Ld, switching means in the lead Lcd which are not shown and earth. Relays T and Y energize. Relay Tbrings the switch IDI to rest in the manner previously described. Relay Y switches through the speaking leads at contacts ity and Iiiy. Contact I'Iy is opened and prevents the switching group selector UGWSII being seized over contacts 6 of a switch of the group I. The switch IDI was able to test at contact 6 because relay JNI is energized. Relay JNI energizes when all the internal group selectors J GW'II to J GWI UI of the group I are engaged as is assumed in the present example.

The calling subscriber on the line La/Lb is now connected to the internal group selector J GWI UII by the aid of the change-over circuit WeI, over which the internal traic oi the group II over contact II) of the switch IDII and following switches of the group II normally passes. Setting of the internal group selector JGWIII takes place with the aid of relays A and B in the known way by the calling stationtransmitting impulses. The group selector itself is not shown because the p-resent invention is not concerned with its construction. If the switch JGWIIIII is already seized over a switch of the group II when the switch IDI is set in position I the latter switch again tests over wiper ddI because guarding potential is connected to lead L04 by applying over wiper ddII. Wiper ddII is connected to switching means which are identical with the switching means connected to lead LdI of the switch IDI.

The control switches ci group II also. have access over their auxiliary rest positions (position 6) to a change-over circuit indicated in the drawings by WeII. This change-over circuit is equipped in the same yway as the change-over circuit WeI of the group I of control switches. The changeover circuit WeII gives access to the control switch UGWGI if when a call is initiated for example .over the control switch IDII (which is indicated) all the switching group selectors which can be reached over contacts I to 5 are'engaged. In this case the switching group selector UGW4I causes an external connecting line to be connected up if the calling station dials the number of such a line. If, however, after the switch UGWIII has been connected up the calling party dials the number characterizing an internal call the switch IDII is .switched over so that it searches for a free outgoing line to an internal group selector over the contacts il] to l. If in the normal progress of a call all the internal group selectors which are connected to contacts "I to I of the switch IDII are engaged when the switch IDII has been switched over the switch likewise passes to position t. In this position it is brought to rest and the switch JGWIIII is connected up. This is an internal group selector which is normally reached from the control switches of group I over their contacts It. The calling station then establishes the desired call over this interval group selector.

By suitable grouping it is, of course, possible to arrange the system so that even in the normal case a control switch of one of 'the' groups has access over individual contacts to switches of the other group by applying known group multipling, etc.

If all the external outlets and the auxiliary switches UGWEII are engaged in the overflow 6 of group I of the control switches relays EXI and K are energized. These relays then control relay G over contacts 'item1 and 26k which by opening its contact llg prevents any seizure over the lead Lc.

What is claimed is:

1. In an automatic switching arrangement, a control switchhaving access to a plurality of lines, said lines being arranged in groups accessible to the wipers of said switch,I means for seizing said switch and for causing said wipers to automatically search for an idle line in one group, an overflow device, means operated to seize said device over the wipers of said switch when all the lines in said one group are busy, and means in said device operated over said wipers for at times causing the lwipers of said control switch to searchforan idle oneof said lines in another of said groups. l

. v2.V An automatic switching arrangement as claimed in claim .1, wherein said means in said deviceatiother 4times kreverts a signal over` the wipers Yof the switchk to indicate that a connection isl unobtainable.

A 3. An automatic switching arrangement as claimed in claimi, wherein said means in said deviceat othertimes controls the extension of arconnectionthrough said device.

Llg-.In :an automatic switching arrangement, a control switchi having .access to groups of lines, an Yoverflow :device accessible to said switch, means for` seizing said switch, for causing same to automaticallysearch for an idle line in one of said .groups,l and, vif all ofthe lines of said one group are-'busyfto connect with said overflow device, means for transmitting digits to said device, means therein'responsive to certain of said .digits forcausing the extension of a connection through said device or responsive to certain other of said digits lfor causing said control switch to search for an idle one o1` said lines in another one of said groupstA c A A -V A Y .5.` In an `automatic switching arrangement, a control switchhaving access to groups oi lines, an overilow device `accessible to said switch,

means for seizing saidl switch, for causing same y .and means .therein for. causing or preventing a further automatic searching operation of said .control switch in accordance with certain of said digits. Y,

In anvautomatic switching arrangement, a

:control switch having access to groups of lines, L

Yan overflow device Vaccessible to said switch, means for seizing said switch, for causing same to automatically Search for ,an idle line in one of said groups, and, if the lines of said one group arebusynto connectwithy said overiiow device,

meansfor transmitting digits over said switch to -said device,y means in said .device responsive thereto forcausingsaid control switch tosearch another group, Said switch effective `to connect .zwith said overflow. device again if said other .z

group is busy, and means operated whensaid de- `vicleisgagain connectedwith to transmit a. signal indicating that a line is unavailable.

7. In` aswitching system, an automaticswitch whose` wipers have access to a plurality of lines, 7;

means for making any of said lines busy, means for causing said switch to search for an idle line and, when one isl found, extend a connection thereto over its wipers, and means for controlling saidswitch revertively over said wipers and said lastline, thereby to cause said switch to move its wipers-from said lastline in search for another idle line.

8. In a switching system, an automatic switch,

equipment accessible to said switch, means for extendinga connection over the wipers'of said 5switch to, said equipment and for transmitting thereto over said .connection one or more digits, meansin said equipment for at times, in demination to cause said pendence upon .the value of said one or more digitsx'imtiating a hunting movement' o f` the wipersof sai'd.switch,`V and means in said equipment for atzo'ther times extendingsaid-connection through said equipment. j A' 9. In a switching system, an automatic switch, equipmentaccess'ible to' saidswitch, means for extendingza :connection over the wipers of'said switchY to said equipmentV and `for transmitting thereto over saidconnection one or more digits, anddiscriminating means in ,said equipmentfor making a determination Afromsaid digits alone, said last means 4effective at times to initiate a movement of the wipers of said switch yirl dependenceaupon said determination.'v Y Y f 10. In` a` -switching system, two groups of trunks, a distributor having access to said trunks,

`means for operatingsaid distributor to seize Van idle trunk of one otsaid groups and for transf mitting to said trunk over said distributor one or more digits, means in said trunk fer et times causing the switch terminating the trunk to extend a connection in accordance with said digits, and 4other means lin saidtrunk effective at times Iin accordance with said digits to cause said distributor todisconnect from said trunk and seize an idle trunl of the other of said groups.

11. lIn a `switching system, two groups of trunks, control equipment, a distributor having access to' said tWo groups of trunks and to said control equipment, means for operating said disl tributor toseize an idle trunk in one of said groups iithere is an idle trunk available in said Aone group or to seize said control equipment if no trunk 4is-.available in said one group, means for ,transmittingover said distributor one or more digits,4 and meansyin said control equipment, if same isseized by saidV distributor, for receiving Seidene ermere digits and matins a determina- -tien therefromy said eentrel equipment `thereupon effective at times in accordance with said deterdistributor to seize an idle trunk in theether of said groups.

12, In a telephone system, outgoing lines, local lines,v a distributor having access to said lines, means for seizing said distributor to extend a call, said distributor effective responsive to said seizure to search for an idle one of said outgoing lines ,and extend a connection thereto, discrimihatingv means associated-with said outgoing line for determining whether the callis local or outgoing and, if same is local,ifo r causingsaid distributor to'searlch for` an idleone of said local lines and extend a connection thereto. 13. In a 'telephone' system, outgoing lines, local lines, discriminating g equipment,` a distributor -herine eeeese te seid lines-end ie. seid equipment ymeans for seizing said distributor to extend a call, means responsive to said seizure for causing said distributor to search for an idle one of said out'- .eeine lilies and .extend .a .eeimeeiiee ihereta'or, if no one` of said outgoing lines is idle, to extend a connection to said discriminating equipment, 4and means-in said equipment for determining whether the call is local or outgoing and, if same is local, forcausing said distributor to search for anid-e one sof-A saidrlocal lines-and extend a conntifn'theeO-n Y l l i i 'HANS DREYER. 

